Wireless communication systems provide for radio communication links to be arranged within the system between pluralities of user terminals. Such user terminals may be mobile and may otherwise be known as subscriber units. At least one other terminal, e.g. used in conjunction with subscriber units, may be a fixed terminal, e.g. a control terminal, base station, or access point. Such a system typically includes a system infrastructure that generally includes a network of various fixed installations such as base stations, which are in direct radio communication with the subscriber units. Each of the base stations operating in the system may have one or more transceivers which may, for example, serve subscriber units in a given local region or area, known as a ‘cell’ or ‘site’, by radio frequency (RF) communication. The subscriber units that are in direct communication with a particular base station are said to be served by the base station, and all radio communications to and from each subscriber units within the system are made via respective serving base stations. Sites of neighbouring base stations in a wireless communication system may be offset from one another or may be overlapping.
Wireless communication systems may operate according to an industry standard land subscriber unit (LMR) protocol such as, for example, the Project 25 (P25) standard defined by the Association of Public Safety Communications Officials International (APCO), the Digital Subscriber unit (DMR) standard, Terrestrial Trunked Radio (TETRA) or other radio protocols. Communications in accordance with DMR, P25, TETRA, or other standards may take place over physical channels in accordance with one or more of a TDMA (time division multiple access) protocol, a FDMA (frequency divisional multiple access), or other protocol. Subscriber units in wireless communication systems such as DMR systems send and receive user communicated voice data (e.g., voice or audio alone or multiplexed with other data such as video or image data) and non-voice data (e.g., location data or sensor data, status updates, control signalling, etc.), herein referred to collectively as ‘traffic information’, in accordance with the designated protocol.
Furthermore, LMR systems may operate in either a conventional or trunked configuration. In either configuration, a plurality of subscriber units may be partitioned into separate groups of subscriber units, such that subscriber units may selectively participate in individual (subscriber unit to subscriber unit) calls and also in group (subscriber unit to many subscriber units) calls.
In a conventional system, each subscriber unit in a group is selected to a particular FDMA frequency for communications associated with that subscriber unit's group. Thus, each group is served by one frequency (e.g., channel), and multiple groups may share the same single frequency (in which case, in some embodiments, group IDs may be present in the group data to distinguish between groups using the same shared frequency). In some systems, each conventional frequency may be further configured to carry multiple logical channels via a TDMA protocol, which allows for multiple concurrent calls on each frequency based on the configured slotting ratio of the TDMA channels (e.g., a slotting ratio of 2 allows 2 distinct logical channels, etc.). Each logical channel may comprise a repeating set of a single time slot or of multiple time slots interleaved with the other remaining logical channels. In addition, some systems may provide an additional conventional channel, sometimes identified as a data revert channel, that is reserved for specific data transmissions such as uplink status or location updates, among other possibilities. Subscriber units desiring to transmit such updates may temporarily move away from their assigned group channel to transmit the updates. In still other systems, subscriber units may use other conventional channels that may be assigned to one or more other groups, but are determined to be currently unused by the one or more other groups, to transmit such updates.
In contrast to conventional systems, a trunked radio system and its subscriber units use a pool of traffic channels (e.g., FDMA or TDMA protocols operating on a plurality of available physical frequencies) for virtually an unlimited number of groups of subscriber units (e.g., talkgroups). Thus, all groups are served by all channels. The trunked radio system works to take advantage of the probability that not all groups need a traffic channel for communication at the same time. When a member of a group requests a call on a control or rest channel on which all of the subscriber units in the system idle awaiting new call notifications and other signalling, in one embodiment, a call controller assigns a separate traffic channel for the requested group call, and all group members move from the assigned control or rest channel to the assigned traffic channel for the group call. In another embodiment, when a member of a group requests a call on a control or rest channel, the call controller may convert the control or rest channel on which the subscriber units were idling to a traffic channel for the call, and instruct all subscriber units that are not participating in the new call to move to a newly assigned control or rest channel selected from the pool of available channels. With a given number of channels, a much greater number of groups can be accommodated in a trunked system as compared with conventional radio systems. In a trunked system, a temporarily assigned or a permanently assigned data revert channel may also be provided for subscriber units to individually transmit updates.
Group members for group calls conducted on conventional or trunked systems may be statically or dynamically defined. That is, in a first example, a user or administrator working on behalf of the user may indicate to the switching and/or radio network (perhaps at a call controller, push-to-talk (PTT) server, zone controller, or mobile management entity (MME), base station controller (BSC), mobile switching center (MRC), site controller, Push-to-Talk controller, or other network device) a list of participants of a group at the time of the call or in advance of the call. The group members (e.g., subscriber units) could be provisioned in the network by the user or an agent, and then provided some form of group identity, identifier, or address, for example. Then, at a future time, an originating user in a group may cause some signalling to be transmitted indicating that he or she wishes to establish a communication session (e.g., group call) with each of the pre-designated participants in the defined group. In another example, subscriber units may dynamically affiliate with a group (and also disassociate with the group) perhaps based on user input, and the switching and/or radio network may track group membership and route new group calls according to the current group membership.
Many wireless communication systems, including many LMR systems, provide for non-voice data transmission on one or more separate dedicated data revert channels, or opportunistically on other available (currently unused) voice or data channels. Such data transmission capabilities may be used to periodically or semi-periodically (e.g., intermittently) report location information of subscriber units, determined via a GPS system, triangulation process, or some other method, or to periodically or semi-periodically report other types of data such as status updates or sensor information. Reported status updates may include whether the subscriber unit or user associated with the subscriber unit is working a particular case, is on the clock or not on the clock, is on a walking beat or patrolling in a vehicle, or many other similar or different types of status updates. Reported sensor information may include environmental conditions surrounding the subscriber unit or health conditions (e.g., pulse rate, temperature, oxygen level, breath rate, etc.) of the subscriber unit's user, amongst many other possibilities. Such status, location, and/or sensor information is usually short in nature (e.g., does not require a large amount of bandwidth to transmit, and can normally be transmitted in under one second), but is reported in a periodic or semi-periodic manner so that infrastructure applications, devices, and/or dispatchers can be provided with updated information over time. Other types of short data may be transmitted as well.
As the number of applications that utilize or depend upon such short data transmissions grow, the number and frequency of such transmissions has grown as well. One problem that has arisen with respect to the transmission of short data from subscriber units during group or individual calls is that calls having an excessive duration impair the ability of any one particular subscriber unit participating in the call from reporting such short data. In other words, while a particular subscriber unit is participating in call activity (e.g., receiving voice, audio, or video to and/or from one or more other subscriber units or from one or more infrastructure devices) it is unable to transmit the short data. As a result, applications, devices, and/or dispatchers in the infrastructure relying upon the short data transmissions are starved of new and/or updated data, which could lead to negative consequences, especially in first responder wireless communications systems.
Accordingly, what is needed is an improved method, device, and system for transmitting short data during an active call by a dual watch subscriber unit.